The electrical quality of lnAs films grown on GaAs substrates by MBE is found to be optimum for growth temperatures close to 490 "C. The Hall mobility for such samples is80000cm2V-'s-' at 77 K for film thicknesses of 5 pm but falls to about 10 000 cm2 V -' s -' at a thickness of 0.05 pm. The carrier concentration in the bulk of the films is believed to be less than 10'5cm-3. The carrier concentration rises and the mobility falls as the growth temperature is varied on either side of this optimum value, reaching 2.5 x 10'8cm-3 and 15000cm2V-'s-' at 77 K respectively for a growth temperature of 350 "C.Extremely sharp free-carrier cyclotron resonance and shallow donor lines are observed from the bulk of the film in far-infrared magneto-optical measurements, together with a very broad but strong cyclotron resonance line from an electron accumulation layer believed to be at the surface. The width of the cyclotron resonance line is consistent with a bulk mobility of the order of 200000cm2V-' 5 -' and the decrease in Hall mobility, together with the apparent increase in carrier concentration with decreasing film thickness, can be explained by the parallel conductance from the two-dimensional electron gas at the surface. There is no evidence for a significant reduction in mobility from the high density of threading dislocations caused by the mismatch with the GaAs substrate. The sharpness of the cyclotron resonance allows an accurate value for the band edge effective mass to be determined of 0.0236 f 0.0003m. with a pressure coefficient of ' +2.0% kbar-'. The donor lines are sufficiently sharp that central cell structure due to two different donor contaminants can be detected, and these donors are thought to be sulphur and selenium originating from the As source material. Certain of the transitions detected are too energetic to be from the shallow donors and these are thought to arise from singly ionized double donors which may be arsenic antisites.Silicon is found to act as a donor dopant up to high concentrations (6 x 10'ecm-3 where the mobility is 2000 cm2 V -' s -' )

A new reflected mode magneto-optic spatial light modulator (R-MOSLM) has been developed for miniature optical correlators and computers. A factor of 4 improvement in pixel switching sensitivity, compared to the conventional transmission mode magneto-optic spatial light modulator, has been achieved by the use of narrower drive lines, and burying the conductor into the film. A factor of 3 higher resolution and a factor of 2 higher optical efficiency have also been achieved by the use of smaller pixels and narrower pixel gaps. The smaller pixels and improved switching sensitivity permit an order of magnitude reduction in optical path length and increase in frame rate, respectively. The progress that has been made in the design of the R-MOSLM, issues concerning its fabrication, a comparison by finite element analysis of field modeling to experimentally determined current requirements to drive individual lines, and some optical characteristics are discussed.

Thin films of bismuth substituted iron garnet are fabricated on silicon (100) substrates using the pulsed laser deposition technique. There is a narrow temperature range in which good polycrystalline garnet films can be grown on silicon; it must be higher than 575 °C for the films to crystallize and lower than 700 °C to avoid chemical reaction between the silicon substrate and the deposited materials. Film microstructure and magnetic properties are compared for films grown at different growth conditions and annealing procedures. The films heated during deposition are smooth and dense in contrast to the post-annealed films, which are characterized by clusters of many smaller grains separated by large cracks and a very small coercivity.

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